The Hydrogen Fuel Alternative

Crabtree, G. W.; Dresselhaus, M. S.

doi:10.1557/mrs2008.84

Cited by 285 publications

(185 citation statements)

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“…The vacuum space was set with 20 Å in the z direction to avoid the interactions between periodic images. For BC 3 substrate, since its primitive cell is about twice the size of graphene's, a (3 Â 3) supercell was used for the modeling. A 3 Â 3 Â 1 mesh of k-points 29 and the global orbital cutoff of 5.0 Å have been used in the spin-unrestricted calculations.…”

Section: ' Computational Methodsmentioning

confidence: 99%

“…For the BC 3 sheet, we investigated the H migration process from the catalytic metal to the supporting substrate, as well as the H diffusion behavior along the CÀC and CÀBÀC paths on G BC 3 . The reaction diagram of each migration/diffusion process is plotted in Figure 5, together with the top views of the critical structures involved in these reactions.…”

Section: H Migration From Ptmentioning

confidence: 99%

“…Second, we estimate the activation barrier for one H atom migrating from Pt 4 to B-doped graphene, and a much lowered migration barrier is obtained due to the enhanced CÀH binding strength around the B atom. Finally, we investigate the hydrogen spillover on the BC 3 sheet with a similar procedure as described above. The uniform BÀC network presents sufficiently low activation barriers for both migration and diffusion of H atoms on the BC 3 substrate.…”

Section: ' Introductionmentioning

confidence: 99%

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DFT Study of Hydrogen Storage by Spillover on Graphene with Boron Substitution

et al. 2011

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The lack of effective hydrogen storage medium has hindered the potential use of hydrogen as fuel for vehicles, personal electronics, and other portable power applications.1À3 Some critical challenges for the storage materials involve high hydrogen storage capacity, ambient temperature operation (0À100°C), reversibility of storage, and fast charge/release kinetics. Various candidates have been investigated, such as carbon materials, 4,5 metalÀorganic frameworks, 6,7 metal hydrides, 8,9 and microporous polymers.10,11 However, no particular material can meet all the requirements thus far.As an effective approach for hydrogen storage at ambient temperature, hydrogen spillover has been experimentally demonstrated by Yang and co-workers on many carbon-based materials, including graphite nanofibers, 12 carbon nanotubes, 12À14 activated carbons, 12,14 metalÀorganic frameworks, 15À17 and covalent-organic frameworks. 17 In these experiments, carbon substrate materials were doped with metal catalysts, which dissociated the H 2 molecules into H atoms. Then the H atoms migrated from metal to the supporting carbon materials and further diffused on the carbon substrate. With this hydrogen spillover process, significant enhancements of hydrogen uptake at 298 K by a factor of ca. 3 were observed, and the storage was found to be reversible with fast rates.However, to fulfill the requirements for hydrogen storage materials, further improvement of hydrogen storage properties of carbon materials is still needed, where a deep understanding of the hydrogen spillover process is of great importance. In this aspect, theoretical calculation can play a leading role and provide helpful information. Cheng et al. have studied the dissociation of molecular hydrogen on the Pt 6 cluster, and by approaching the fully saturated Pt 6 cluster toward the graphene sheet, they proposed a migration of two H atoms from metal to graphene, with an average activation barrier of 0.48 eV per H atom; however, thermodynamically, the migration process is endothermic. 18 Further investigation by Froudakis et al. about hydrogen spillover on Pt-doped graphite, which is the real case in experiments in which metal clusters are supported on the substrate, showed a rather higher migration barrier of 2.6 eV for H atom diffusing from a fully saturated Pt 4 cluster to the supporting graphitic surface.19 Yakobson et al. also pointed out that it is difficult for a pristine graphene to attract the H atom down from the saturated metal catalyst, due to the weak CÀH binding strength for the pristine graphene, which greatly inhibits the spillover process at ambient temperature. 20 So, how to improve the CÀH binding or the hydrogen adsorption strength on the graphitic surface naturally becomes one of the crucial points in hydrogen spillover research. ABSTRACT: The hydrogen spillover mechanism on B-doped graphene was explicitly investigated by first-principles calculations. By the incorporation of boron into graphene, our theoretical investigation shows that B doping can substanti...

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Section: ' Computational Methodsmentioning

confidence: 99%

Section: H Migration From Ptmentioning

confidence: 99%

Section: ' Introductionmentioning

confidence: 99%

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DFT Study of Hydrogen Storage by Spillover on Graphene with Boron Substitution

et al. 2011

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“…Given our modular approach, the choice of supporting electrolyte was determined by measuring the Faradaic efficiency for each electrode/electrolyte configuration independently before being implemented into the PV-EC device. For example, when operating the NiMoZn cathode for HER at current densities of 10 mA cm -2 , GC analysis showed no hydrogen production, indicating that NO 3 -is preferentially reduced as opposed to protons. Alternatively, using K 2 SO 4 as a supporting electrolyte results in a Faradaic efficiency of 100% (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…Coupling photovoltaics to drive catalytic fuelforming reaction, such as water splitting to generate H 2 , allows for direct solar-to-fuels conversion. The solar-generated H 2 can effectively be harnessed to electricity by fuel cell devices (3,4) or converted to liquid fuels upon its combination with CO or CO 2 (5)(6)(7). For this technology to be effectively implemented, a solar-to-fuels conversion efficiency (SFE) of 10% or higher is desirable (8,9).…”

mentioning

confidence: 99%

Ten-percent solar-to-fuel conversion with nonprecious materials

Cox

Lee

Nocera

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

297

233

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Direct solar-to-fuels conversion can be achieved by coupling a photovoltaic device with water-splitting catalysts. We demonstrate that a solar-to-fuels efficiency (SFE) > 10% can be achieved with nonprecious, low-cost, and commercially ready materials. We present a systems design of a modular photovoltaic (PV)-electrochemical device comprising a crystalline silicon PV minimodule and lowcost hydrogen-evolution reaction and oxygen-evolution reaction catalysts, without power electronics. This approach allows for facile optimization en route to addressing lower-cost devices relying on crystalline silicon at high SFEs for direct solar-to-fuels conversion.istributed and grid-scale adoption of nondispatchable, intermittent, renewable-energy sources requires new technologies that simultaneously address energy conversion and storage challenges (1, 2). Coupling photovoltaics to drive catalytic fuelforming reaction, such as water splitting to generate H 2 , allows for direct solar-to-fuels conversion. The solar-generated H 2 can effectively be harnessed to electricity by fuel cell devices (3, 4) or converted to liquid fuels upon its combination with CO or CO 2 (5-7). For this technology to be effectively implemented, a solar-to-fuels conversion efficiency (SFE) of 10% or higher is desirable (8, 9).Direct photoelectrochemical (PEC) water splitting by a single absorber material has attracted a vast amount of attention (10, 11), and recent progress indicates improvements in the field (12, 13); but after decades of research, direct PEC faces three challenges to increase conversion efficiency: (i) Direct absorber band alignment is required to provide carriers with appropriate potential to both half reactions. Although such an alignment is difficult to achieve in a single material initially, any change in band alignment due to changing surface conditions can result in further efficiency degradation. This makes it challenging to design devices that maintain robust, high efficiencies in actual operation.(ii) The wide absorber bandgap (>1.23 eV; typically >1.6 eV) needed to drive the water-splitting reaction is not optimized for the solar spectrum, which results in a maximum SFE of only 7% (14-16). (iii) The absorbers are poor catalysts, and they are incapable of efficiently performing the four proton-coupled electron transfer chemistry (17-22) that is needed for water splitting.These deficiencies can be overcome by substituting a PEC device with a buried-junction photovoltaic (PV) device and an electrochemical catalyst (EC) system, forming a PV-EC tandem (23-27). In a buried-junction device, the electric field is generated at an internal junction within the semiconductor and is then coupled with water-splitting catalysts through ohmic contacts, which can either be conductive coatings directly deposited onto the PV or connected through wires to the electrodes. The buried junction relaxes the constraints imposed by a PEC device because it separates light absorption from catalysis, and does not require that the absorber be stable in ...

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Fuel Cells: Proton Exchange Membranes

Devanathan

2005

Encyclopedia of Inorganic Chemistry

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Proton exchange membrane, also known as polymer electrolyte membrane, fuel cells (PEMFCs) offer the promise of efficient conversion of chemical energy of fuel, such as hydrogen or methanol, into electricity with minimal pollution. Their widespread use to power zero‐emission automobiles as part of a hydrogen economy can contribute to enhanced energy security and reduction in greenhouse gas emissions. However, the commercial viability of PEMFC technology is hindered by high cost associated with the membrane‐electrode assembly (MEA) and poor membrane durability under prolonged operation at elevated temperature. Membranes for automotive fuel cell applications need to perform well over a period comparable to the life of an automotive engine and under heavy load cycling including start‐stop cycling under subfreezing conditions. The combination of elevated temperature, changes in humidity levels, physical stresses, and harsh chemical environment contribute to membrane degradation. Perfluorinated sulfonic acid (PFSA)‐based membranes, such as Nafion ® , have been the mainstay of PEMFC technology. Their limitations, in terms of cost and poor conductivity at low hydration, have led to continuing research into membranes that have good proton conductivity at elevated temperatures above 120 °C and under low‐humidity conditions. Such membranes have the potential to avoid catalyst poisoning, simplify fuel cell design, and reduce the cost of fuel cells. Hydrocarbon‐based membranes are being developed as alternatives to PFSA membranes, but concerns about chemical and mechanical stability and durability remain. Novel anhydrous membranes based on polymer gels infused with protic ionic liquids have also been recently proposed, but considerable fundamental research is needed to understand proton transport in novel membranes and evaluate durability under fuel cell operating conditions. In order to advance this promising technology, it is essential to rationally design the next generation of PEMs on the basis of an understanding of chemistry, membrane morphology, and proton transport obtained from experiment, theory, and computer simulation.

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The Hydrogen Fuel Alternative

Cited by 285 publications

References 42 publications

DFT Study of Hydrogen Storage by Spillover on Graphene with Boron Substitution

DFT Study of Hydrogen Storage by Spillover on Graphene with Boron Substitution

Ten-percent solar-to-fuel conversion with nonprecious materials

Fuel Cells: Proton Exchange Membranes

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